Reciprocating engine of a spark ignition type

ABSTRACT

A spark ignition type reciprocating engine of a natural intake system with an ignition plug arranged to face a combustion chamber defined and delimited by a piston inserted into a cylinder so as to move in a reciprocating way, which has: 
     a bore size of the cylinder ranging from approximately 45 mm to 67 mm; 
     a volume of a single chamber of the cylinder ranging from approximately 110 cc to 340 cc; 
     a ratio of a stroke of the piston to the bore size of the cylinder being larger than 1; and 
     a compression ratio of the engine being 11 or larger.

This application is a division of U.S. application Ser. No. 08/345,344,filed Nov. 21, 1994, now U.S. Pat. No. 5,445,123, which is acontinuation of Ser. No. 07/936,001, filed Aug. 27, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reciprocating engine of a sparkignition type and, more particularly, to a spark ignition typereciprocating engine of a natural intake system with ignition plugsdisposed so as to face combustion chambers of the engine.

2. Description of the Related Art

Among engines of a natural intake system, i.e. internal combustionengines without superchargers, spark ignition type reciprocating enginesare loaded on many automobiles, each of which is provided with ignitionplugs so as to face the combustion chambers defined and delimited by thepistons inserted into the cylinders so as to be movable in areciprocating way. It is well known that the engines of this type canprovide better heat efficiency as a compression ratio becomes larger.

It can be noted, however, that there is the tendency that knockingbecomes likely to occur when a larger compression ratio is set. Forconventional engines except for engines so adapted as to be suitable foruse with a so-called high-octane gasoline having a large octane value, acompression ratio (ε) is set at largest to ε=about 10.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a sparkignition type reciprocating engine of a natural intake system so adaptedas to set a compression ratio larger than a conventional compressionratio while preventing knocking from occurring.

In order to achieve the aforesaid object, the present invention consistsof a spark ignition type reciprocating engine of a natural intake systemwith an ignition plug disposed so as to face a combustion chamberdefined and delimited by a piston inserted into a cylinder so as to bemovable in a reciprocating manner, wherein the compression ratio of theengine is set to 11 or over (ε≧11) and wherein a diameter of a bore ofthe cylinder (hereinafter referred to briefly as "the bore size") rangesfrom approximately 45 mm to 67 mm; a volume of a single chamber of thecylinder ranges from approximately 110 cc to 340 cc; and a ratio of astroke of the piston, S, to the diameter of the bore of the cylinder, B,is set to a value larger than 1.

When the problem with knocking is solved the compression ratio of theengine must be set to 11 or over (ε≧11), it is found effective that thebore size of the cylinder is set to the smallest possible size toshorten the distance over which flames develop and expand and in orderto improve anti-knocking performance.

Two limitations are considered when making the bore size smaller. First,there is a reliability limitation related to the speed of the piston asit moves through the cylinder. Second, a limit results from a rapidincrease in the resistance to intake air due to choking associated withthe shortening of a valve size of an intake valve. Hence, the bore sizeis set to the smallest diameter within a range that satisfies these twolimits. Selection of a bore size that satisfies the two limits will nowbe described.

Limit upon reliability (the speed of the piston):

A mean speed of the piston Um (mm per second) can be represented by theformula (1) as follows:

    Um=(N/30)×S

where N is the speed of rotation of the engine in rpm; and

S is the stroke of the piston in millimeters.

A limit value of the mean speed of the piston, Um, is usually 20 m/s(Um=2.0×10⁴ mm per second).

Thus, the formula (1) above can give the stroke of the piston bysubstituting 2.0×10⁴ mm/s for Um and the maximum speed of rotation ofthe engine for N.

Limit from resistance to intake air (choking):

It is generally known that resistance to intake air increases rapidlywhen a mean intake air mach number, Mim, becomes Mim=0.5, therebydecreasing volume efficiency rapidly.

The mean intake air mach number, Mim, can be represented by thefollowing formula (2) as follows: ##EQU1## where Vh is the volume of thesingle chamber as represented in cc;

η_(v) is the efficiency in volume as represented in %;

a is the sonic speed as represented in cm per second;

θ is the angle of a crank as represented in deg, CA. ATDC;

θ_(IC) is the timing for closing the intake valve;

θIO is the timing for opening the intake valve;

N is the speed of rotation of the engine as represented in rpm;

Fi is the area of the opening of the intake valve as represented in cm²; and

Fim(e) is the mean area of the opening of the intake valve asrepresented in cm².

The mean area of the opening of the intake valve, Fim(e), can berepresented by the formula (3) as follows:

    Fim(e)=Fia(e)/(θ.sub.IC -θ.sub.IO)

where Fia(e) is the effective angular area of the intake valve.

Then, the effective angular area of the intake valve, Fia(e), can berepresented by the formula (4) as follows: ##EQU2## where Fi is the areaof the opening of the intake valve.

FIG. 18 shows the result of computation on the effective angular area ofthe intake valve, Fia(e), for the internal combustion engine having twointake valves and two exhaust valves for each cylinder, provided thatthe result of the computation is based on the assumption as follows:

(a) the two intake valves have the same valve sizes;

(b) the two exhaust valves have the same valve sizes; and

(c) a ratio of an area of the intake valve to an area of the exhaustvalve at their throat portions is 1.5 to 1.

Further, the conditions for computing the effective angular area of theopening of the intake valve, Fia(e), are as follows:

(1) the distance between the valve seat of the first intake valve andthe valve seat of the second intake valve is 2.5 mm or over;

(2) the distance between the valve seat of the intake valve and thevalve seat of the exhaust valve is 3.5 mm or over;

(3) the distance between the valve seat of the first exhaust valve andthe valve seat of the second exhaust valve is 4.0 mm or over;

(4) the distance between the valve seat of the intake valve and anignition plug is 2.5 mm or over;

(5) the distance between the valve seat of the exhaust valve and theignition plug is 3.5 mm or over;

(6) the valve seat may come into contact with a peripheral portion ofthe bore of the cylinder;

(7) the angle between the valves is 30°;

(8) the combustion chamber is of a penthouse type;

(9) the diameter of the plug is 14 mm;

(10) the diameter of a stem is 6 mm;

(11) the diameter of the throat portion=the diameter of the valve seatminus 5 mm;

(12) the length of a valve lift is 8.5 mm; and

(13) the timing for opening the valve is 256 deg CA.

The relation between the bore size and the volume of the single chamber,which satisfy the two limits as have been described hereinabove, will beconsidered in the procedures as will be described hereinafter.

Procedure 1: The stroke of the piston can be given from the formula (1)above when the speed of rotation of the engine is determined, whichreaches Um=20 m/s (2.0×10⁴ mm per second) that is the limit value of themean speed of the piston, Um. Further, the volume of the single chamberfor each of the bore sizes can be given on the basis of the given strokeof the piston. FIG. 19 indicates the relation of the bore size with thevolume of the single chamber that reaches Um=2.0×10⁴ mm per second; inFIG. 19, the one-dot-and-dash lines indicate the volumes of the singlechamber corresponding to each of the bore sizes when the speeds ofrotation of the engine are varied by each 1,000 rpm in the range from5,000 rpm to 8,000 rpm.

Procedure 2: The volumes of the single chamber, which reach the meanintake air mach number Min=0.5 with respect to each bore size, are givenfrom the formulas (1) to (4) above and the result of computation on theeffective angular area of the intake valve Fia(e). In FIG. 19, the solidlines indicate the volumes of the single chamber given in Procedure 2for every 1,000 rpm of the speed of rotation of the engine in the rangefrom 5,000 rpm to 8,000 rpm.

Procedure 3: A description will be made of the relation between thespeed of rotation of the engine that results in the mean speed of thepiston being Um=20 m/s (2.0×10⁴ mm per second), hereinafter referred toas "the speed of rotation of the engine N₂₀ ", and the speed of rotationof the engine that results in the mean intake air mach number Mim=0.5,hereinafter referred to as "the speed of rotation of the engine No.₀.5".

(1) If the speed of rotation of the engine N₀.5 is larger than the speedof rotation of the engine N₂₀, the bore size is set so as to allow asufficient amount of the intake air to enter up to a speed higher thanthe limit upon reliability as described hereinabove. Hence, this is tothe contrary of the original purpose that the bore size should be madesmaller, so that the speed of rotation of the engine N₀.5 should beequal to or smaller than the speed of rotation of the engine N₂₀.

(2) It can be noted that the speed of rotation of the engine thatproduces the maximum horse power is generally set to the speed ofrotation of the engine lower by approximately 1,000 rpm than the limitupon reliability.

It should be noted, however, that, if the speed of rotation of theengine becomes higher than the speed of rotation of the engine N₀.5, aflow of intake air per unit time does not increase, so that an axialoutput of the engine does not increase or it is decreased to a largeextent at the speed of rotation of the engine which is equal to orhigher than the speed of rotation of the engine N₀.5.

From the foregoing, it can be said that the point that produces themaximum horse power exists at the speed of rotation of the engine slowerthan the speed of rotation of the engine N₀.5.

For example, if the difference between the speed of rotation of theengine N₀.5 and the limit upon reliability would exceed 2,000 rpm (N₂₀-N₀.5 >2,000), the horse power does not increase, or it is reduced, in aregion where the speed of rotation of the engine is higher by 2,000 rpmor more than the speed of rotation of the engine at which the maximumhorse power is produced. Hence, this case is not good so that the speedof rotation of the engine N₀.5 and the speed of rotation of the engineN₂₀ should satisfy the relation that satisfies N₂₀ -N₀.5 ≦2,000 rpm.

(3) When the characteristics of the engine are to be set in the samemanner as conventional engines, it is preferred that the speed ofrotation of the engine that produces the maximum horse power should beset to larger than 6,000 rpm. Hence, the speed of rotation of the engineN₀.5 should be set to larger than 6,000 rpm.

(4) In order to ensure the predetermined volume in the single chamberand to minimize the bore size, it is necessary to place a limit upon thestroke of the piston. However, it is not desirable to minimize the boresize by shortening the stroke of the piston to an extent that results inthe speed of rotation of the engine significantly exceeding the speed ofrotation of a conventional engine. Hence, the speed of rotation of theengine N₂₀ should be set to 8,000 rpm or slower.

All the conditions given in the procedures as have been describedhereinabove are described in FIG. 19. As shown in FIG. 19, the hatchedarea indicates an area wherein the engine having two intake valves andtwo exhaust valves for each cylinder meets the relation of the bore sizevs. the volumes of the single chamber, which satisfies the aforesaid twolimits. Hence, it is found from FIG. 19 that the bore size ranges fromapproximately 51 mm to 67 mm and the volume of the single chamber rangesfrom approximately 150 cc to 340 cc.

Likewise, a review has been made of the engine having three intakevalves and two exhaust valves for each cylinder under the sameprocedures as have been described hereinabove. As shown in FIG. 19, thecross-hatched area indicates an area that meets the relation of the boresizes with the volumes of the single chamber, which satisfies the twolimits as have been described hereinabove. It is found from FIG. 19 thatthe bore size ranges from approximately 45 mm to 50 mm and the volume ofthe single chamber is in the range of from approximately 110 cc to 200cc.

From the foregoing results, the range in which the bore size can beminimized is from approximately 45 mm to 67 mm and the range in whichthe predetermined volume of the single chamber can be ensured is fromapproximately 110 cc to 340 cc.

Further, it should be noted that a ratio of the stroke of the piston, S,to the bore size of the cylinder, B, is larger than one, i.e. S/B>1. Inother words, the engine has a long stroke and the bore size is madesmaller in order to ensure the same volumes in each of the singlechambers. This arrangement can minimize a load upon a bearing of a crankshaft.

Other objects, features and advantages of the present invention willbecome apparent in the course of the description of the preferredembodiments, which follows, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing an embodiment of thespark ignition type reciprocating engine according to the presentinvention.

FIG. 2 is a sectional plan view taken along line II--II of FIG. 1.

FIG. 3 is a schematic representation showing an intake system and anexhaust system of the internal combustion engine according to thepresent invention.

FIG. 4 is a block diagram showing a control system of the internalcombustion engine according to the present invention.

FIG. 5 is a map for controlling a shutter valve disposed in an intakepassage.

FIG. 6 is a diagram describing the action of a variable valve timing ina region I.

FIG. 7 is a diagram describing the action of the variable valve timingin a region II.

FIG. 8 is a diagram describing the action of the variable valve timingin a region III.

FIG. 9 is a control map for exhaust gas recirculation (EGR).

FIG. 10 is a control map for performing the control of the shutter valveand the control of the EGR.

FIG. 11 is a diagram showing a comparison between the internalcombustion engine according to the embodiment of the present inventionand the conventional engine on the basis of the S/B ratio vs.displacement.

FIG. 12 is a diagram showing a comparison between the internalcombustion engine according to the embodiment of the present inventionand the conventional engine on the basis of the bore size of thecylinder vs. displacement.

FIG. 13 is a diagram showing a comparison between the internalcombustion engine according to the embodiment of the present inventionand the conventional engine on the basis of the number of cylinders vs.displacement.

FIG. 14 is a diagram showing a comparison of the number of cylindersbetween the internal combustion engine with two intake valves and twoexhaust valves for each cylinder according to the embodiment of thepresent invention and the conventional engine on the basis of the boresize vs. displacement

FIG. 15 is a schematic representation showing an internal combustionengine with a sub-chamber according to a variant of the embodiment ofthe present invention.

FIG. 16 is a diagram showing the timing for opening and closing asub-chamber valve of the internal combustion engine with thesub-chamber.

FIG. 17 is a graph showing the relation of temperatures vs. the specificheat at constant volume.

FIG. 18 is a graph showing the relation (the result of computation)between the bore sizes vs. the effective angular area of the intakevalve, Fia(e).

FIG. 19 is a diagram showing the relation between the bore sizes and thevolumes of the single chamber, suitable for the spark ignition typereciprocating engine according to the present invention.

FIG. 20 is a schematic plan view showing the spark ignition typereciprocating engine with three intake valves and two exhaust valves,according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described more in detail with reference tothe accompanying drawings.

Structure of Engine:

As shown in FIGS. 1 and 2, a body 1 of the engine has a left-hand bankportion 2L and a right-hand bank portion 2R arranged in a V-shapedrelationship. Three cylinders, collectively referred to as 4, arearranged in each of the left-hand and right-hand bank portions 2L and 2Rin line with each of the bank portions. In other words, the internalcombustion engine to be employed for the embodiment of the presentinvention is a so-called V-type 6-cylinder engine. In the descriptionwhich follows, reference symbols "L" and "R" used as suffixes, asneeded, are intended to mean "left-hand" and "right-hand", respectively.

A detailed description will be made of the body 1 of the engine. Thebody 1 of the engine has a cylinder block 3 and each of the cylinders 4has a combustion chamber 8 of a penthouse type formed and delimited by apiston 6 inserted into a cylinder section 5 and a cylinder head 7. Asspecifically shown in FIG. 1, the cylinder head 7 is provided with firstand second intake ports 9 and 10 as well as first and second exhaustports 11 and 12, each having an opening at the combustion chamber 8. Asfurther shown in FIG. 1, a first intake valve 13 is mounted to the firstintake port 9 and a second intake valve 14 is mounted to the secondintake port 10; and a first exhaust valve 15 is mounted to the firstexhaust port 11 and a second exhaust valve 16 is mounted to the secondexhaust port 12.

The body 1 of the engine to be employed in this embodiment of thepresent invention is a 4-valve type engine having two intake valves 13and 14 and two exhaust valves 15 and 16 for each cylinder. Avalve-operating system 17 for operatively opening and closing the valves13-16 is of a so-called double overhead cam (DOHC) type, which has twocam shafts 18 and 19 accommodated in the cylinder head 7. In otherwords, the first cam shaft 18 is adapted to operatively open and closethe intake valves 13 and 14, and the second cam shaft 19 is adapted tooperatively open and close the exhaust valves 15 and 16. As shown inFIG. 2, each of the first and second cam shafts 18 and 19 is provided atits shaft end with a cam pulley 20 for the intake valve (although a campulley for the exhaust valve is not shown in the drawing). The campulley 20 is mechanically associated with an output shaft (a crankshaft) 23 of the engine through a timing belt 22, in a manner as isknown to the art, thereby opening and closing the intake valves 13, 14and the exhaust valves 15, 16 at a predetermined timing, insynchronization with the rotation of the output shaft 23 of the engine.

To the first cam shaft 18 is mounted a first valve timing change-overmechanism 24 (for the intake valves) for changing a phase of the firstcam shaft 18 for the cam pulley 20 for the intake valves, and the secondcam shaft 19 is provided with a second valve timing change-overmechanism (for the exhaust valves) for changing a phase of the secondcam shaft 19 for the cam pulley for the exhaust valves, although notshown in the drawing. The second valve timing change-over mechanism forthe exhaust valves has the same structure as the first valve timingchange-over mechanism 24 for the intake valves so that a description ofdetails of the second valve timing change-over mechanism will be omittedfrom the description which follows. To each of the cylinder heads 7 ismounted an ignition plug 25 so as to face or direct to the center of thecombustion chamber 8.

The piston 6 is connected to the crank shaft 23 through a connecting rod26, and a chamber 28 for reserving or storing engine oil is formed by anoil pan 29 in a region underneath a crank chamber 27 for accommodatingthe crank shaft 23. In FIG. 2, reference numeral 30 denotes an oilstrainer.

Above each of the left-hand and right-hand bank portions 2L and 2R isdisposed a surge tank 34 extending lengthwise along the crank shaft 23,and the surge tank 34 is connected to the intake ports 9 and 10 for eachcylinder 4 through a discrete intake tube 35. As an upstream end of eachof the intake ports 9 and 10 in the respective left-hand and right-handbank portions 2L and 2R is disposed so as to open facing an centralspace 31 interposed between the bank portions, the discrete intake tube35 is arranged in such a shape as firstly extending transversely fromthe surge tank 34 toward the central space 31 and then curving downward.

A detailed description will now be made of an intake system 40 for thebody 1 of the engine with reference to FIG. 3.

The intake system 40 comprises a common intake tube 41, the left-handsurge tank 34L, the right-hand surge tank 34R, and the discrete intaketube 35, which are disposed in this order from the upstream side towardthe downstream side. To the common intake tube 41 are disposed an aircleaner 42, an air flowmeter 43, and a throttle valve 44 in this orderfrom the upstream side toward the downstream side. The common intaketube 41 has a bypass 45 disposed so as to bypass the throttle valve 44.

The bypass 45 is provided with an ISC valve 47 which in turn can adjustthe number of idling rotation in a manner as is known to the art. On theother hand, the left-hand surge tank 34L is communicated with theright-hand surge tank 34R through a connecting tube 50 which in turn isprovided in its intermediate position with a valve 51 for controllingintake air variably, for example, thereby opening and closing the valve51 in accordance with the number of rotation of the engine and achievingthe dynamic effect of intake air over a wide region in a manner as isknown to the art.

The discrete intake tube 35 is provided with a partition wall 35a tothereby divide its internal space partially into left-hand andright-hand sections, i.e. a first discrete intake tube 52 and a seconddiscrete intake tube 53. The first discrete intake tube 52 is connectedwith the first intake port 9, and the second discrete intake tube 53 isconnected with the second intake port 10. The second discrete intaketube 53 is so arranged as to be opened or closed with a shutter valve 54mounted at its upstream end portion. Each of the shutter valves 54Ldisposed in the left-hand bank portion 2L is connected with a commonshaft 55L for the left-hand bank portion 2L, and each of the shuttervalves 54R disposed in the right-hand bank portion 2R is connected witha common shaft 55R for the right-hand bank portion 2R. To a shaft end ofeach of the common shafts 55L and 55R is mounted an actuator (notshown).

A fuel supply system of the body 1 of the engine comprises an electronicinjector 57 which in turn is mounted in the discrete intake tube 35 soas to face the first intake port 9 and the second intake port 10. InFIG. 3, reference numeral 58 denotes an assist air passage and referencenumeral 59 denotes a check valve.

As shown in FIG. 3, an exhaust system 60 of the engine comprises aleft-hand exhaust manifold 61L for the left-hand bank portion 2L, aright-hand exhaust manifold 61R for the right-hand bank portion 2R, anda common exhaust tube 62, which are disposed in this order from theupstream side toward the downstream side. The common exhaust tube 62 isprovided in its intermediate position with a catalyst converter 63 forcleaning exhaust gases and at its downstream end with a silencer (notshown) in a manner as is known to the art.

The body 1 of the engine has a first outer EGR passage 65 and a secondouter EGR passage 66, and a transversely sectional diameter of the firstouter EGR passage 65 is smaller than that of the second outer EGRpassage 66. The first outer EGR passage 65 is so adapted as to beemployed in a low load region, while the second outer EGR passage 66 isso adapted as to be employed in a high load region, as will be describedhereinafter.

The first outer EGR passage 65 is connected at its one end to theexhaust manifold 61L or 61R and at its other end to the first intakeport 9. To the first outer EGR passage 65 are mounted a first EGR valve67 on its one end side and a collective chamber 68 on its other endside. The collective chamber 68 is communicated with the common intaketube 41 through a bypass air tube 69 to which a bypass air control valve70 in turn is mounted. On the other hand, one end of the second outerEGR passage 66 is connected to the common exhaust tube 62 on the sidedownstream of the catalyst converter 63, and the other end thereof isconnected to the common intake tube 41 on the side downstream of thethrottle valve 44. The second outer EGR passage 66 is provided from theone end side to the other end side with a carbon trap 71, an EGR cooler72, and a second EGR valve 73.

Specification of Engine:

A specification of the engine is as follows:

(1) Type of engine: V-type 6-cylinder; DOHC 4-valve engine

(2) Angle between the left-hand bank portion and the right-hand bankportion: 90°

(3) Displacement: 1,496 cc

(4) Bore size of cylinder: 63 mm in diameter

(5) Stroke of piston: 80 mm

(6) Compression ratio (ε): ε=12 (although ε=11 is also acceptable)

(7) Angle between the intake valve and the exhaust valve: 30°

(8) Fuel: regular gasoline (octane value=91)

In other words, the spark ignition type reciprocating engine accordingto the embodiment of the present invention has the cylinder section 5with a small bore size and a long stroke wherein the stroke of thepiston is larger with respect to the bore size. Further, the engine hasa high compression ratio.

The engine has a control unit U as shown in FIG. 4, and the control unitU is comprised of, for example, a microcomputer. Into the control unitU, signals are entered from the air flowmeter 43 for sensing an amountof intake air, a sensor 80 for sensing an angle of the opening of thethrottle valve 44, and a sensor 81 for sensing the number of rotation ofthe engine. On the other hand, the control unit U generates controlsignals to the shutter valve 54, the electronic injector 57, the firstEGR valve 67, the second EGR valve 73, and the first valve timingchange-over mechanism 24 for the intake valves.

Control of Shutter Valve 54:

The shutter valve 54 is so arranged as to be closed in a low rotationregion where the number of rotation of the engine is lower than, forexample, 3,000 rpm and opened in a high rotation region where the numberof rotation of the engine is higher than, for example, 3,000 rpm. Insuch a low rotation region where the amount of intake air is smaller, onthe one hand, the intake is performed by opening the first discreteintake tube 52 only while closing the second discrete intake tube 53. Inthe high rotation region where the amount of intake air becomes larger,on the other hand, the intake is performed by opening both of the firstand second discrete intake tubes 52 and 53.

Control of Valve Timing:

The valve timing for regions I, II and III will be described withreference to the map as indicated in FIG. 5.

Region I: The region I is a region where the load of the engine is lowand the number of rotation of the engine is low. As shown in FIG. 6,reference symbol "EV" denotes the exhaust valve and reference symbol"IV" denotes the intake valve (this being applied to FIGS. 7 and 8).

In this region, the valve timing for opening the exhaust valves 15 and16 is set at 70 deg (crank angle) before the bottom dead center (BBDC)while the valve timing for closing them is set at 10 deg (crank angle)after the top dead center (ATDC); on the other hand, the valve timingfor opening the intake valves 13 and 14 is set at 20 deg (crank angle)after the top dead center (ATDC) while the valve timing for closing themis set at 80 deg (crank angle) after the bottom dead center (ABDC).

Region II: This region is a region where the load of the engine is belowtwo thirds of the load.

In the region II, as shown in FIG. 7, the valve timing for opening theexhaust valves 15 and 16 is set at 40 deg (crank angle) before thebottom dead center (BBDC) and the valve timing for closing them is setat 40 deg (crank angle) after the top dead center (ATDC). On the otherhand, the valve timing for opening the intake valves 13 and 14 is set at20 deg (crank angle) after the top dead center (ATDC) and the valvetiming for closing them is set at 80 deg (crank angle) after the bottomdead center (ABDC).

Region III: This region is a region where the load of the engine isabove two thirds of the load.

In the region III, as shown in FIG. 8, the valve timing for opening theexhaust valves 15 and 16 is set at 70 deg (crank angle) before thebottom dead center (BBDC) and the valve timing for closing them is setat 10 deg (crank angle) after the top dead center (ATDC). On the otherhand, the valve timing for opening the intake valves 13 and 14 is set at10 deg (crank angle) before the top dead center (BTDC) and the valvetiming for closing them is set at 50 deg (crank angle) after the bottomdead center (ABDC).

In summary, the intake valves 13 and 14 are set so as to be delayed inclosing in such partially loaded regions. Specifically, in the region I,the intake valves 13 and 14 are opened after the exhaust valves 15 and16 have been closed; alternatively, an overlap of an open state of theintake valve with an open state of the exhaust valve is set to besmaller than in the region II and III. In the region II, an overlap ofthe range of the crank angle, at which the exhaust valves 15 and 16 areopen, with the range of the crank angle, at which the intake valves 13and 14 are open, is larger than an overlap of the open state of theintake valve with the open state of the exhaust valve in the region III.In the region III, an overlap of the crank angle, at which the exhaustvalves 15 and 16 are open, with the crank angle than that in the regionI and smaller than that in the region II.

The foregoing description can be briefed as follows:

(1) Region I (with the low load of the engine and the low number ofrotation of the engine): the overlap is zero or smaller and the closingof the intake valves is delayed.

(2) Region II (with the load of the engine smaller than two thirds ofthe entire load): the overlap is zero and the closing of the intakevalves is delayed.

(3) Region III (with the Load of the engine larger than two thirds ofthe entire load): the overlap is the same and the timing of closing theintake valves is the same as conventional ones.

Control of EGR:

The control of the recirculation of exhaust gases (EGR) is performed inthree regions, i.e. region I, IV, and V, on the basis of the map asindicated in FIG. 9 by controlling the first EGR valve 67 and the secondEGR valve 73 in a fashion as will be described hereinafter.

Region I: This region is a region wherein the load of the engine is lowand the number of rotation of the engine is low, as have been describedhereinabove.

In this region I, both of the first and second EGR valves 67 and 73 areclosed.

Region IV: This region is a region wherein the load of the engine issmaller than two thirds of the total amount of the load.

In the region IV, a rate of the EGR is adjusted by the first EGR valve67 while the second EGR valve 73 is closed. In other words, exhaustgases are recirculated by taking advantage of the first outer EGRpassage 65.

Region V: This region is a region in which the load of the engine isover the full range from the region larger than two thirds of the totalload up to the total amount of the load.

In the region V, a rate of the EGR is adjusted by the second EGR valve73 while the first EGR valve 67 is closed. In other words, exhaust gasesare recirculated by the aid of the second outer EGR passage 72 with theEGR cooler 72. Further, in this region, the rate of the EGR is soarranged as to be constant or to be increased as the load becomeslarger.

It is to be noted that FIG. 10 is prepared by a combination of FIG. 5indicative of the control of the valve timing with FIG. 9 indicative ofthe control of the EGR. In FIG. 10, the region is divided into fourregions, I, VI, VII and VIII. A detailed description will be made of theregions I, VI and VIII, where the problems arise with stability incombustion, fuel economy or knocking. The engine is controlled in theseregions in such a manner as will be described hereinafter.

Region I: This region is a region in which the load is extremely light,that is, the load is low and the number of rotation of the engine islow, as described hereinabove. In the region I, combustion is likely tobecome unstable.

In this region, an outer EGR via the outer EGR passages is inhibited andthere is no overlap or a smaller overlap between the crank angle atwhich the exhaust valves 15 and 16 are open and the crank angle at whichthe intake valves 13 and 14 are open. Hence, the amount of gases whichare left in the combustion chamber 8 is so small that the stability incombustion can be ensured. Further, as the angle at which the throttlevalve 44 is open is small in the region I, the closing of the intakevalves 13 and 14 is delayed, so that a loss in pumping can be reduced.

Region VI: This region is a region where the load is light, or the loadof the engine is lower than two thirds of the total amount of the load.

In the region VI, the combustion is relatively stable, so that anoverlap of the crank angle at which the exhaust valves 15 and 16 areopen with the crank angle at which the intake valves 13 and 14 are openis set to be larger. Hence, an internal EGR is performed in addition tothe recirculation of exhaust gases from the first outer EGR passage 65.In other words, in the region VI, as the overlap of the range in whichthe exhaust valves 15 and 16 are open with the range in which the intakevalves 13 and 14 are open so as to become large, the internal EGR iscarried out by causing a large amount of gases to be remained in thecombustion chamber 8. The exhaust gases to be remained in the combustionchamber 8 for the internal EGR are high in temperature. Further, theexhaust gases to be recirculated through the first outer EGR passage 65are relatively high in temperature because the exhaust gases withdrawnfrom the engine are recirculated to the engine through the first outerEGR passage 65 whose upstream end is communicated with the exhaustmanifold 61, before they are allowed to become cool.

In addition, the closing of the intake valves 13 and 14 is delayed, sothat the delay in closing them in combination with the recirculation ofthe exhaust gases having higher temperature can reduce a loss in pumpingin the region VI.

Region VIII: This region contains the whole region of the load of theengine higher than two thirds of the total amount of the load thereof.

In the region VIII, the overlap of the range of the crank angles atwhich the exhaust valves 15 and 16 are open with the range of the crankangles at which the intake valves 13 and 14 are open is so conventionaland the timing of closing the intake valves is so conventional that aircan be filled in the combustion chamber in an appropriate way. Inaddition, in the region VIII, the exhaust gases are allowed to cool withthe second outer EGR passage 66 with the EGR cooler 72 and thenrecirculated, i.e. a so-called cold EGR is performed, therebysuppressing the temperature within the cylinder from elevating.

In the region VIII, the temperature within the cylinder can be loweredin the way as described hereinabove by means of scavenging, delaying theclosing of the intake valves 13 and 14, and the cold EGR, so that anoccurrence of knocking can be suppressed and the amount of NOx withinthe exhaust gases can be decreased in the region VIII.

It is to be noted that FIGS. 11 to 13 indicate each a comparison of thecharacteristics of the engine according to the present invention andconventional ones. As is apparent from FIG. 11, it is found that theengine according to the present invention has a stroke longer than theconventional ones; it is found from FIG. 12 that the bore size is smallwith respect to the displacement; and it is further found from FIG. 13that the number of cylinders is large with respect to the displacement.

Hence, the engine according to the present invention having thecharacteristics as described hereinabove can achieve improvements inheat efficiency and fuel economy while suppressing the knocking fromoccurring by making the bore size smaller and the compression ratiohigher. Further, the engine according to the present invention canreduce a burden imposed upon the bearing units, thereby reducing amechanical loss. In addition, the engine with multiple cylindersaccording to the present invention can make an internal combustionengine with less vibration.

Further, it is to be noted that the engine according to the presentinvention can provide a variety of internal combustion engines with thenumber of cylinders varied without alteration of the configuration ofeach one of the cylinders. FIG. 14 indicates a comparison of the engineswith four, six and eight cylinders with conventional engines.

For the engine according to the present invention, the temperaturewithin the cylinder may be lowered by injecting water into thecombustion chamber 8 in the high load region in order to further preventthe knocking from occurring in the high load region. The lower thetemperature within the cylinder the more completely the knocking can beprevented, that is, the more difficult it is to cause the knocking tooccur, and the higher the compression ratio can be made.

Further, a sub-chamber 90 may be disposed in the body 1 of the engine asa means for preventing an occurrence of knocking, as shown in FIG. 15.In FIG. 15, the same elements are provided with the same referencenumerals as those shown in FIG. 1 and other drawings and a descriptionof those elements will be omitted from the explanation which follows.

Engine with Sub-chamber (FIG. 15):

The sub-chamber 90 disposed in the body 1 of the engine is provided witha sub-chamber port 90a having an opening in the combustion chamber 8,and a sub-chamber valve 91 is mounted at the sub-chamber port 90a. Inthe high load region (as indicated by the region V in FIG. 9), thesub-chamber port 90a is so arranged as to be opened or closed with thesub-chamber valve 91. On the other hand, in the low load region (asindicated by the regions I and IV in FIG. 9), the sub-chamber port 90ais so arranged as to be closed with the sub-chamber valve 91.

FIG. 16 shows an example of the timing of opening and closing thesub-chamber port 90a with the sub-chamber valve 91 in the high loadregion.

As is apparent from FIG. 16, the timing of closing the sub-chamber port90a with the sub-chamber valve 91 is the same as the timing of ignition,i.e. 160 deg after the bottom dead center (ABDC), and the sub-chamberport 90a is opened at approximately 70 deg before that closing timing,thereby allowing the mixed air within the sub-chamber 90 to be replacedwith the mixed air within the combustion chamber 8.

It can further be noted that the timing of opening the sub-chamber valve91 may preferably be in the process of the stroke of compression,particularly in the middle stage, and the timing of closing it maypreferably be substantially the same as or somewhat earlier than thetiming of ignition, although the timing of closing the sub-chamber valve91 may be set in the initial stage of the stroke of explosion. Further,the volume of the sub-chamber 90 may be set to be from approximately 20%to 50% of the volume of the combustion chamber at the top dead center,and the area of the sub-chamber valve 91 may be set to be fromapproximately 20% to 30% of the area of the intake valve.

The arrangement for the engine as have been described hereinabove allowsa portion of the mixed fuel within the combustion chamber 8 to be closedin the sub-chamber 90 with the sub-chamber valve 91 so disposed as to beopened or closed during the stroke of compression, and the portion ofthe mixed fuel is then cooled in the sub-chamber 90 and then replacedwith a portion of the mixed fuel within the combustion chamber 8 duringthe stroke of compression which follows, thereby lowering thetemperature within the cylinder in the high load region to a level lowerthan that of the conventional engines with no sub-chamber equippedtherewith and suppressing the knocking from occurring.

An internal combustion engine is so designed as to translate an increasein pressure (a rate of elevation of the pressure within the cylinder,ΔP) associated with the combustion of the fuel fed to its combustionchamber into mechanical work. Hence, the internal combustion engine cando better work as the rate of elevation of the pressure within thecylinder, ΔP, becomes larger. Given the combustion at a constant volume,the rate of elevation of the pressure within the cylinder, ΔP, can berepresented by the formula (1) as follows:

    ΔP=(εR/V)×(Q/Cv)                       (1)

where

ε is the compression ratio;

R is the gas constant;

Q is the heat capacity of fuel;

V is the volume of the combustion chamber; and

Cv is the specific heat at a constant volume.

A review will now be made of an impact of changes in temperature uponthe rate of elevation of the pressure within the cylinder, ΔP.Differentiation of the formula (1) above gives the formula (2) asfollows:

    d(ΔP)/dT=-(εR/V)×(Q/Cv.sup.2)×(dCv/dT)(2)

It can be noted herein that the specific heat at a constant volume, Cv,becomes larger as the temperature is made higher, as indicated in FIG.17. Hence, the expression, (dCv/dT), of the right side of the formula(2) above is larger than 0 (zero) so that the right side of the formula(2) above gives a negative value.

Hence, the expression, d(ΔP)/dT, of the left side of the formula (2)above gives a negative value; in other words, the higher the temperaturewithin the cylinder the smaller the rate of elevation of the pressurewithin the cylinder, ΔP. This means that the lower the temperaturewithin the cylinder, the higher the rate of elevation of the pressurewithin the cylinder, ΔP, and the better job the engine can do.

The fact that the engine can do better work as the temperature withinthe cylinder becomes lower may be described from another point of view.

The heat capacity Q of fuel can be represented by the formula (3) asfollows:

    Q=Cv×G×ΔT                                (3)

where

Cv is the specific heat at a constant volume;

G is the mass of the mixed fuel charged into the combustion chamber; and

ΔT is the rate of elevation of temperature associated with combustion(the rate of elevation of the temperature within the cylinder).

The formula (3) above can be modified into the formula (4) as follows:

    ΔT=Q/(Cv×G)                                    (4)

As is understood from the formula (4) above, the rate of elevation ofthe temperature, ΔT, becomes higher as the specific heat at a constantvolume, Cv, is made smaller, provided that the heat capacity of thefuel, Q, and the mass of the mixed fuel charged into the combustionchamber are set constant.

It can be noted that the specific heat at a constant volume, Cv, becomeslarger as the temperature T is made higher, as shown in FIG. 17. Inother words, the lower the temperature within the cylinder, T, thesmaller the specific heat at a constant volume, Cv; hence, the lower thetemperature within the cylinder, T, the higher the rate of elevation ofthe temperature within the cylinder, ΔT, associated with the combustion.

Since the pressure within the cylinder is caused to be raised at alarger rate of elevation of the pressure within the cylinder, ΔP, as therate of elevation of the temperature within the cylinder, ΔT, becomeshigher, the rate of elevation of the pressure within the cylinder, ΔP,becomes larger as the temperature within the cylinder, T, is lower. Inother words, if the same amount of the heat capacity would be created bythe same amount of fuel charged, it can be noted that, as thetemperature within the cylinder, T, is made lower, the rate of elevationof the pressure within the cylinder, ΔP, becomes higher, thereby doingbetter work and giving better heat efficiency.

As will be apparent from the foregoing description, the provision of thesub-chamber 90 in the body 1 of the engine permits the knocking to besuppressed from occurring in the high load region as well as improvesthe heat efficiency in the high load region.

When the elevation of the temperature associated with the compression ofthe mixed fuel within the combustion chamber is to be utilized to themaximum extent, the timing of closing the sub-chamber valve 91 is set tobe at the top dead center of compression. Alternatively, when theelevation of the pressure associated with the combustion is to beutilized to the maximum extent, the timing of closing the sub-chambervalve 91 is set as late as possible. It can be noted herein that theangle of the crank at which the pressure associated with the combustionreaches the maximum is generally at approximately 30 deg after the topdead center of compression (ATDC).

It is generally known that actual states of combustion vary largely withcycles. If the sub-chamber valve 91 would be kept open until a deviationof the pressures within the cylinder becomes large, it is undesirablethat the pressure, the density, and the temperature of the mixed fuelenclosed within the sub-chamber 90 may vary in each of cycles. Hence, ifthe sub-chamber valve 91 would be closed immediately before theoccurrence of the deviation in the elevation of the pressure associatedwith the combustion, the impact of the deviation in the combustion canbe suppressed, and the effect of cooling the mixed fuel can be improved.

Variant of Engine with Sub-chamber:

The knocking is unlikely to occur as the load of the engine becomeslighter (in the light load region). If the heat efficiency is to beimproved in the light load region by lowering the temperature within thecylinder, however, the valve timing of opening and closing thesub-chamber valve 91 may be conveniently changed by the aid of the valvetiming change-over mechanism in such a manner that the valve timing ofopening and closing the sub-chamber valve 91 is set so as to approachthe valve timing of closing the intake valves 13 and 14 in accordancewith the load as the load becomes smaller. This arrangement can suppressthe loss of the pressure associated with the introduction of the mixedfuel into the sub-chamber 90 to a minimum extent and it can improve theheat efficiency due to a decrease in the temperature within thecylinder.

As a means for forcibly lowering the temperature of the mixed fuelwithin the sub-chamber 90, a movable piston may be mounted within thesub-chamber 90, which is so arranged as to displace within thesub-chamber 90 in synchronization with the rotation of the crank shaft23, thereby causing the mixed fuel to flow in the sub-chamber 90.Alternatively, the movable piston may be so biased with a spring as toforcibly cause the substantial volume of the sub-chamber 90 to be madesmaller, when the sub-chamber valve 91 is opened, thereby causing themixed fuel passing through the sub-chamber port 90a to flow or move.

Other Means for Preventing Knocking (Lean Burn):

For a lean-burn engine wherein the air-fuel ratio is leaner than thestoichiometric air-fuel ratio, a portion of the heat capacity producedby the combustion is absorbed by a surplus of the air, thereby loweringthe temperature within the cylinder, T. The leaner the air-fuel ratio,the larger the surplus amount of the air. This makes the temperaturewithin the cylinder, T, lower, thereby making the knocking unlikely tooccur and improving the heat efficiency. Further, actually, thereduction of the temperature within the cylinder reduces thetransmission of heat to the wall surface of the combustion chamber andit can decrease the loss in cooling. Hence, the leaner air-fuel ratiocan reduce the loss in cooling and as a result it can improve the heatefficiency.

For example, even if the air-fuel ratio would be set to as extremelylean as A/F=30, ignitability and combustibility can be ensured by makingthe intake port 9 in a swirl port or in a tumble port or by making thecompression ratio larger in accordance with the lean extent of theair-fuel ratio or by igniting at multiple points.

Although the region in which the engine is running in a lean air-fuelratio may be set so as to cover all the region in which the engine isrunning, the engine is driven in a lean air-fuel ratio, for example, inthe constantly running region, particularly in the middle-rotational andmiddle load region. In the region other than the region where the engineis running in such a lean air-fuel ratio, it can be driven, for example,in the stoichiometric air-fuel ratio. Specifically, the engine is run inthe lean air-fuel ratio in the regions VI and VII of FIG. 10, althoughthe engine may be run in these regions, given the number of rotation ofthe engine being set to a predeter-mined value, e.g. 4,000 rpm orslower. In the regions I and VIII, the engine is run in thestoichiometric air-fuel ratio.

FIG. 20 shows an example of an engine having three intake valves and twoexhaust valves; reference numeral 101 stands for a combustion chamber;reference numerals 102, 103 and 104 for intake ports; reference numerals105, 106 and 107 for intake valves; reference numerals 108 and 109 forexhaust ports; reference numerals 110 and 111 for exhaust valves; andreference numeral 112 for an ignition plug.

As described hereinabove, the spark ignition type reciprocating engineaccording to the present invention can make the bore size smaller withrespect to the volume of the single chamber, thereby suppressing theknocking from occurring and setting the compression ratio larger thanthe conventional ones. Further, the engine according to the presentinvention has a longer stroke, so that it can reduce a burden to beimposed on the bearing section of the crank shaft.

The present invention is not intended in any manner to be limited to theembodiments as described hereinabove, and it is to be understood thatany variations or modifications made so as not to deviate from the basicconcepts of the present invention are interpreted as being containedwithin the spirit of the present invention.

What is claimed is:
 1. A spark ignition type reciprocating engine of anatural intake type system with an ignition plug disposed to face acombustion chamber defined and delimited by a piston inserted into acylinder so as to move in a reciprocating way, further comprising:meansfor reducing an effective compression ratio of the engine in a regionwhere a load on the engine is relatively low so as to make the effectivecompression ratio lower than in a region where a load on the engine isrelatively high; wherein a ratio of a stroke of the piston to a boresize of the cylinder is chosen to be larger than 1 so that knocking inthe engine tends not to occur in the region where the load on the engineis relatively high; and wherein the engine has a compression ratio of atleast
 11. 2. A spark ignition type reciprocating engine as claimed inclaim 1, wherein the bore size is relatively small.
 3. A spark ignitiontype reciprocating engine as claimed in claim 2, wherein the bore sizeis 70 mm or less.
 4. A spark ignition type reciprocating engine asclaimed in claim 1, wherein said means for reducing an effectivecompression ratio comprises a valve timing change-over mechanism forchanging a timing of closing an intake valve of the combustion chamber.5. A spark ignition type reciprocating engine as claimed in claim 2,wherein said means for reducing an effective compression ratio comprisesa valve timing change-over mechanism for changing a timing of closing anintake valve of the combustion chamber.
 6. A spark ignition typereciprocating engine as claimed in claim 3, wherein said means forreducing an effective compression ratio comprises a valve timingchange-over mechanism for changing a timing of closing an intake valveof the combustion chamber.
 7. A spark ignition type reciprocating engineas claimed in claim 4, wherein said valve timing change-over mechanismis further operable to change an overlap of an open state of the intakevalve with an open state of an exhaust valve of the combustion chamberin accordance with a running state of the engine.
 8. A spark ignitiontype reciprocating engine as claimed in claim 5, wherein said valvetiming change-over mechanism is further operable to change an overlap ofan open state of the intake valve with an open state of an exhaust valveof the combustion chamber in accordance with a running state of theengine.
 9. A spark ignition type reciprocating engine as claimed inclaim 4, wherein said valve timing change-over mechanism is operable toclose the intake valve relatively later when a load on the engine isrelatively low and to close the intake valve relatively sooner when theload on the engine is relatively high.
 10. A spark ignition typereciprocating engine as claimed in claim 7, wherein said valve timingchange-over mechanism is operable to close the intake valve relativelylater when a load on the engine is relatively low and to close theintake valve relatively sooner when the load on the engine is relativelyhigh.
 11. A spark ignition type reciprocating engine as claimed in claim1, wherein said means for reducing an effective compression ratio of theengine reduces a pumping loss of the engine when the load on the engineis relatively low by reducing the effective compression ratio of theengine in the region where the load on the engine is relatively low. 12.A spark ignition type reciprocating engine as claimed in claim 1,wherein the means for reducing the effective compression ratio of theengine, the ratio of the stroke of the piston to the bore size of thecylinder being larger than 1 and the compression ratio of the enginebeing at least 11 together ensure that the engine effectively convertscombustion energy to engine power as the load on the engine varies frombeing relatively low to relatively high.
 13. A method of configuring aspark ignition type reciprocating engine having a natural intake typesystem with an ignition plug disposed to face a combustion chamberdefined and delimited by a piston inserted into a cylinder so as to movein a reciprocating way, the method comprising:including in the enginemeans for reducing an effective compression ratio of the engine when aload on the engine is relatively low so as to make the effectivecompression ratio lower than when the load on the engine is relativelyhigh; reducing knocking in the engine when the load on the engine isrelatively high by configuring a stroke of the piston and a bore size ofthe cylinder so that a ratio of the stroke of the piston to the boresize of the cylinder is larger than 1; and configuring the engine tohave a compression ratio of at least
 11. 14. The method of claim 13,further comprising configuring the bore size to be 70 mm or less. 15.The method of claim 13, further comprising configuring the means forreducing an effective compression ratio as a valve timing change-overmechanism operable to change a timing of closing an intake valve of thecombustion chamber.
 16. The method of claim 15, further comprisingconfiguring the valve timing change-over mechanism to change an overlapof an open state of the intake valve with an open state of an exhaustvalve of the combustion chamber in accordance with a running state ofthe engine.
 17. The method of claim 15, further comprising configuringthe valve timing change-over mechanism to close the intake valverelatively later when a load on the engine is relatively low and toclose the intake valve relatively sooner when the load on the engine isrelatively high.